product is small, and the phases can be well controlled, which makes this method to
have good prospects for development.
6.3.3 Sol–Gel Method
Sol–gel method is a commonly used method for synthesis of amorphous and
crystalline TiO 2 nanomaterials for the sake of its advantages such as processing at
low temperature and the ability to prepare materials in various morphologies.
Titanium alkoxides or titanium halides are usually used as the titanium precursor
Fig. 6.6 Proposed mechanism: (a) the orientation of the third octahedron determines the formation
of rutile or an anatase nucleus; (b) interaction between SO 4
2À anion and TiO 6
2À octahedral
hydroxyls; (c) two TiO 6
2À octahedra share edge when SO 4
2À is present; (d) the formation of
anatase in the presence of SO 4
2À [66]. (Reprinted with permission from Ref. [66]. Copyright 2005,
American Chemical Society)
6.3 Synthesis of Mixed-Phase TiO 2 Photocatalysts
145